Secondary batteries and power consumption devices

Abstract

A secondary battery and a power consumption device are disclosed. The secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a first active layer disposed on at least one surface of the negative electrode current collector, the first active layer including first graphite and a first silicon-carbon composite, the first graphite having a flatness of ≥ 2, and the first silicon-carbon composite including a porous carbon substrate and a silicon-based material disposed within the pores of the porous carbon substrate.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to a Chinese patent application filed on July 31, 2023, bearing application number 2023109522472 and entitled "Secondary Battery and Power Consumption Device," the entire contents of which are incorporated herein by reference.

[0002] This application relates to the field of secondary battery technology, and more particularly to secondary batteries and power consuming devices. [Background technology]

[0003] The statements herein merely provide background information related to the present application and may not necessarily constitute prior art.

[0004] Silicon-based materials have a relatively high gram capacity, and their application to the negative electrode of a secondary battery can provide the battery with a relatively high energy density. However, after charging, the volume expansion of silicon-based materials is relatively large, which reduces the cycle performance of the battery. Summary of the Invention

[0005] The present application provides a secondary battery including a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer including a first active layer including first graphite and a first silicon-carbon composite, the first graphite having a flatness of ≥ 2, and the first silicon-carbon composite including a porous carbon substrate and a silicon-based material located in pores of the porous carbon substrate.

[0006] In the secondary battery, the first graphite having a flatness of ≥ 2 is used in combination with the first silicon carbon composite to buffer the volume expansion of the silicon carbon composite during charging, improve the stability of the electrode structure, and further improve the cycle performance of the battery.

[0007] In some embodiments, the flatness of the first graphite is 2.5 to 20. When the flatness of the first graphite is in this range, the stability of the electrode plate structure can be further improved. Optionally, the flatness of the first graphite is 4 to 16.

[0008] In some embodiments, the first graphite comprises primary particles. The primary particles have a relatively suitable flatness, which is advantageous for improving the pressure resistance of the first active layer. Optionally, the number ratio of the primary particles in the first graphite is ≥ 90%.

[0009] In some embodiments, the volume average particle diameter Dv50 of the first graphite is 12 μm to 18 μm. A volume average particle diameter Dv50 of the first graphite within this range is advantageous for obtaining a relatively large compaction density. Optionally, the volume average particle diameter Dv50 of the first graphite is 14 μm to 16 μm.

[0010] In some embodiments, the specific surface area of ​​the first graphite is 0.6 m 2 / g~1.4m 2 / g. The specific surface area of ​​the first graphite within this range can provide an appropriate porosity, further improving the energy density of the secondary battery, while allowing the electrolyte to be in sufficient contact with the first active layer, thereby achieving good dynamic performance. Optionally, the specific surface area of ​​the first graphite is 0.8 m 2 / g~1.2m 2 / g.

[0011] In some embodiments, the first graphite includes artificial graphite and / or natural graphite. Artificial graphite has good cycle performance and is advantageous for improving the cycle performance of a secondary battery. Natural graphite has good pressure resistance and is advantageous for improving the pressure resistance of a first active layer. Optionally, the first graphite includes natural graphite, and the mass percentage of the natural graphite in the first graphite is ≦20%.

[0012] In some embodiments, the volume average particle diameter Dv50 of the first silicon carbon composite is 5 μm to 13 μm. If the volume average particle diameter Dv50 of the first silicon carbon composite is too large, it may limit the charging performance of the secondary battery. If the volume average particle diameter Dv50 of the first silicon carbon composite is too small, the first active layer may become relatively brittle, causing cracks in the negative electrode plate during charging, which may affect the battery's performance. Optionally, the volume average particle diameter Dv50 of the first silicon carbon composite is 7 μm to 11 μm.

[0013] In some embodiments, the specific surface area of ​​the first silicon carbon composite is greater than 1 m 2 / g~8m 2 / g. If the specific surface area of ​​the first silicon carbon composite is too large, the cycle performance and storage performance may be unfavorable. If the specific surface area of ​​the first silicon carbon composite is too small, the porosity of the first silicon carbon composite may be relatively small, and the dynamic performance of the battery may be unfavorable. Optionally, the volume average particle diameter Dv50 of the first silicon carbon composite is 1 m 2 / g~5m 2 / g.

[0014] In some embodiments, the mass percentage of the first silicon carbon composite in the first active layer is 5% to 50%. If the mass percentage of the first silicon carbon composite in the first active layer is too small, the improvement in the effect of improving the energy density of the battery is not significant. If the mass percentage of the first silicon carbon composite is too large, the improvement in the effect of improving the compaction density is not significant.

[0015] In some embodiments, the mass percentage of the porous carbon substrate in the first silicon carbon composite is ≧40%. If the mass percentage of the porous carbon substrate in the first silicon carbon composite is too low, the electrical conductivity of the first silicon carbon composite may be unfavorable, and the battery performance may be unfavorable. If the mass percentage of the porous carbon substrate is too high, the mass percentage of the corresponding silicon-based material may be too low, and the improvement in battery energy density may not be significant. Optionally, the mass percentage of the porous carbon substrate in the first silicon carbon composite is 40% to 60%.

[0016] In some embodiments, the porosity of the porous carbon substrate is 30% to 60%. If the porosity of the porous carbon substrate is too low, the dynamic performance of the battery may be unfavorable. If the porosity of the porous carbon substrate is too high, the cycle performance and storage performance of the battery may be unfavorable.

[0017] In some embodiments, the mass percentage of the silicon-based material in the first silicon carbon composite is ≦60%. If the mass percentage of the silicon-based material in the first silicon carbon composite is too high, the voltage resistance of the first active layer may be poor. At the same time, if the mass percentage of the silicon-based material is too high, the expansion coefficient of the first silicon carbon composite material may increase, and the structural stability of the negative electrode plate may be poor during charging. Optionally, the mass percentage of the silicon-based material in the first silicon carbon composite is 40% to 60%.

[0018] In some embodiments, the silicon-based material comprises nanosilicon, and optionally, the nanosilicon has a grain size of ≦6 nm. In the first silicon carbon composite, the nanosilicon has a relatively small grain size, which can provide the first silicon carbon composite with good cycling performance.

[0019] In some embodiments, the negative electrode active layer further comprises a second active layer located on a surface of the first active layer away from the negative electrode current collector, the second active layer comprising second graphite. The provision of the second active layer can further improve the overall compaction density of the negative electrode plate.

[0020] In some embodiments, the surface of the second graphite is coated with a carbon coating layer. The provision of the carbon coating layer can improve the overall conductivity of the second graphite and can improve the fast charging performance of the secondary battery. Optionally, the thickness of the carbon coating layer is 10 nm to 300 nm, and more optionally, 20 nm to 100 nm.

[0021] In some embodiments, the second graphite includes secondary particles. The introduction of secondary particles can further improve the charging performance of the secondary battery. Optionally, the number ratio of the secondary particles in the second graphite is ≧50%, and optionally 50% to 90%.

[0022] In some embodiments, the volume average particle diameter Dv50 of the second graphite is smaller than the volume average particle diameter Dv50 of the first graphite. The relatively small volume average particle diameter Dv50 of the second graphite can reduce the lithium ion transport pathways, which is advantageous for improving the dynamic performance of the negative electrode plate and further improving the fast charging performance of the battery. Optionally, the volume average particle diameter Dv50 of the second graphite is 9 μm to 15 μm, and more preferably 11 μm to 13 μm.

[0023] In some embodiments, the specific surface area of ​​the second graphite is greater than the specific surface area of ​​the first graphite, which is advantageous for improving the cycle performance of the battery. Optionally, the specific surface area of ​​the second graphite is greater than 0.8 m 2 / g~1.6m 2 / g, and more selectively 1m 2 / g~1.4m 2 / g.

[0024] In some embodiments, the second active layer further comprises a second silicon carbon composite. The second active layer further comprises a second silicon carbon composite, which can further improve the energy density of the secondary battery. Optionally, the material of the second silicon carbon composite comprises the material of the first silicon carbon composite.

[0025] In some embodiments, the mass percentage of the second silicon carbon composite in the second active layer is 5% to 50%. If the mass percentage of the second silicon carbon composite in the second active layer is too small, the improvement in the effect of improving the energy density of the battery is not significant. If the mass percentage of the second silicon carbon composite is too large, the improvement in the effect of improving the compaction density is not significant.

[0026] The present application further provides a power consuming device including the secondary battery. [Brief explanation of the drawings]

[0027] In order to more clearly explain the technical solution of the present application, the following briefly introduces the drawings used in the present application. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts. [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery shown in FIG. 1 according to the embodiment of the present application. [Figure 3]

[0023] Figure 1 is a schematic diagram of a power consumption device powered by a secondary battery according to one embodiment of the present application. Reference may be made to one or more drawings to better describe and explain the embodiments and / or examples of those inventions disclosed herein. Additional details or examples for the purposes of illustrating the drawings should not be considered to limit the scope of any of the disclosed inventions, the presently described embodiments and / or examples, and the best modes of those inventions as currently understood. DETAILED DESCRIPTION OF THE INVENTION

[0028] To facilitate understanding of the present application, the following more fully describes the present application with reference to the associated drawings. The drawings illustrate preferred embodiments of the present application. However, the present application may be embodied in many different forms and is not limited to the embodiments set forth herein. Rather, the purpose of providing these embodiments is to provide a more thorough and complete understanding of the disclosure of the present application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms used herein are for the purpose of describing specific examples only and are not intended to be limiting of the present application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0030] The "ranges" disclosed herein may be defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the endpoints, and any endpoint may be independently inclusive or exclusive, and any combination is possible; i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are further listed as maximum range values, the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range of "a to b" represents a shorthand representation of any combination of real numbers a to b, where a and b are both real numbers. For example, a numerical range of "0 to 5" represents a list of all real numbers between "0 and 5" already listed in this specification, and "0 to 5" is merely a shorthand representation of a combination of these numbers. Furthermore, expressing a parameter as an integer ≧2 is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, expressing a parameter as an integer selected from "2 to 10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0031] As used herein, unless otherwise limited, the terms "plurality," "plurality," and the like refer to a number greater than or equal to 2. For example, "one or more" refers to one or more than two.

[0032] Unless otherwise stated, all embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0033] An "embodiment" referred to in this specification means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment or embodiment of the present application. The appearances of this phrase in various locations in the specification do not necessarily all refer to the same embodiment, nor are they mutually exclusive independent or alternative embodiments of other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this specification can be combined with other embodiments. The term "embodiment" referred to in this specification has a similar meaning.

[0034] As will be understood by those skilled in the art, in each embodiment or example method, the order of steps described does not imply a strict execution order or constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible underlying logic. Unless otherwise specified, all steps in this application may be performed sequentially or randomly, and in some examples, are performed sequentially. For example, when a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, when a method described above may further include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0035] In this application, open technical features or technical solutions described with words such as "comprise," "include," or "comprise" do not exclude additional members other than the enumerated members, unless otherwise specified, and can be considered to provide not only a closed feature or solution consisting of the enumerated members, but also an open feature or solution including additional members in addition to the enumerated members. For example, when A includes a1, a2, and a3, unless otherwise specified, it may further include other members or may not include additional members, and can be considered to provide not only a feature or solution in which "A is composed of a1, a2, and a3," but also a feature or solution in which "A not only includes a1, a2, and a3, but also includes other members."

[0036] In this application, unless otherwise specified, it can be understood that A (for example, B) means that B represents one non-limiting example of A, and that A is not limited to B.

[0037] In this application, "optionally", "optional" and "optionally" refer to the possibility of being present or absent, that is, to selecting one of the two parallel solutions of "present" or "absent". When "optionally" appears in multiple places in a technical solution, unless otherwise specified and unless there is a contradictory or mutually restrictive relationship, the "option" in each clause is independent.

[0038] One embodiment of the present application provides a secondary battery including a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer including a first active layer, the first active layer including a first graphite and a first silicon-carbon composite, the first graphite having a flatness of ≥ 2, the first silicon-carbon composite including a porous carbon substrate and a silicon-based material located in the pores of the porous carbon substrate. In this embodiment, the secondary battery uses a combination of the first graphite and the first silicon-carbon composite, each having a flatness of ≥ 2, to buffer the volume expansion of the silicon-carbon composite during charging, thereby improving the stability of the electrode plate structure and further improving the cycle performance of the battery.

[0039] At the same time, the first graphite with a flatness of ≥ 2 is used in combination with the first silicon carbon composite to mitigate the brittleness of the silicon carbon composite during charging, further improving the stability of the electrode plate structure.

[0040] In the present application, the flatness is expressed as the ratio of the major axis to the thickness of a particle, where the smallest size is the thickness, the largest size is the major axis, and the intermediate size is the minor axis. In other words, the flatness of the first graphite represents the ratio of the major axis to the thickness of the first graphite particle.

[0041] In this application, the flatness can be tested as follows: first, a plate is cut into pieces of 6 millimeters (mm) × 6 mm, and then attached to an ion polishing machine and cut at a voltage of 7.5 kilovolts (kV) for 30 minutes (min). Then, in accordance with the JY / T010-1996 test standard, a Sigma300 scanning electron microscope and spectrometer are used to observe and test the flatness of at least 20 graphite particles. The ratio of the longest diameter to the thickness of each graphite particle is calculated and averaged to obtain the corresponding graphite flatness.

[0042] Optionally, the first graphite includes sheet graphite. Further optionally, the first graphite includes flake graphite.

[0043] In some embodiments, the flatness of the first graphite is 2.5 to 20. When the flatness of the first graphite is in this range, the stability of the electrode plate structure can be further improved. Optionally, the flatness of the first graphite may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc. Optionally, the flatness of the first graphite is 4 to 16. For example, the flatness of the first graphite may be in the range of 2 to 8, 2 to 4, 4 to 8, etc.

[0044] In some embodiments, the surface of the first graphite does not include a carbon coating layer. Applying a carbon coating to the first graphite can improve the overall conductive performance of the first graphite and potentially improve the fast charging performance of the battery. However, the introduction of a carbon coating layer can increase the overall hardness of the first graphite and limit the improvement of the compaction density of the first active layer.

[0045] In some embodiments, the first graphite comprises primary particles. The primary particles have a relatively suitable flatness, which is advantageous for improving the pressure resistance of the first active layer. Optionally, the number ratio of the primary particles in the first graphite is ≥ 90%. For example, the number ratio of the primary particles in the first graphite is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc. Even more optionally, the number ratio of the primary particles in the first graphite is 95% to 100%.

[0046] In some embodiments, the first graphite further comprises secondary particles, and the proportion of the secondary particles in the first graphite is ≦10%. When the first graphite further comprises secondary particles, it has a certain effect on improving the fast charging performance of the secondary battery. However, compared to primary particles, secondary particles have a relatively high sphericity, and if the proportion of the secondary particles in the first graphite is too high, the improvement in the pressure resistance performance of the first active layer is limited. Optionally, the proportion of the secondary particles in the first graphite is ≦9%, ≦8%, ≦7%, ≦6%, ≦5%, ≦4%, ≦3%, ≦2%, or ≦1%, etc.

[0047] As some examples of particle size selection for the first graphite, the volume average particle size Dv50 of the first graphite is 12 micrometers (μm) to 18 μm. Having the volume average particle size Dv50 of the first graphite within this range is advantageous for obtaining a relatively large compaction density. Alternatively, the Dv50 of the first graphite is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm. More preferably, the Dv50 of the first graphite is 14 μm to 16 μm.

[0048] It can be understood that in this application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number of particles in the volume cumulative distribution curve when the cumulative particle size distribution number reaches 50%, and its physical meaning is that particles with a particle size smaller (or larger) than that particle size account for 50%. For example, Dv50 can refer to the GB / T 19077-2016 test method, and Dv50 can be obtained using the particle size distribution curve obtained by the laser diffraction particle size distribution analyzer Mastersizer3000.

[0049] As some examples of the selection of the specific surface area of ​​the first graphite, the specific surface area of ​​the first graphite is 0.6 square meters per gram (m 2 / g)~1.4m 2 / g. When the specific surface area of ​​the first graphite is within this range, it is possible to provide an appropriate porosity, further improve the energy density of the secondary battery, and at the same time, allow the electrolyte to be in sufficient contact with the first active layer, thereby achieving good dynamic performance. Optionally, the specific surface area of ​​the first graphite is 0.6 m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g or 1.4m 2 / g. More preferably, the specific surface area of ​​the first graphite is 0.8 m 2 / g~1.2m 2 / g.

[0050] In this application, the specific surface area can be measured based on the specific surface area of ​​a solid material by referring to GB / T 19587-2004 gas adsorption BET method, and can be measured by the nitrogen gas adsorption specific surface area analytical test method and calculated by the Brunauer Emmett Teller (BET) method. The nitrogen gas adsorption specific surface area analytical test can be performed by a Micromeritics TniStar11 3020 specific surface area and pore analyzer.

[0051] In some embodiments, the first graphite comprises artificial graphite and / or natural graphite. Artificial graphite has good cycle performance and is advantageous for improving the cycle performance of the secondary battery. Natural graphite has good pressure resistance and is advantageous for improving the pressure resistance of the first active layer.

[0052] Optionally, the first graphite includes natural graphite, and the mass percentage of the natural graphite in the first graphite is ≦20%. If the amount of natural graphite used is relatively large, there may be a limit to the improvement in battery cycling performance. Further optionally, the mass percentage of the natural graphite in the first graphite is ≦18%, ≦15%, ≦12%, ≦10%, ≦8%, ≦5%, ≦2%, or ≦1%, etc.

[0053] As some selected examples of particle diameters of the first silicon carbon composite, the volume average particle diameter Dv50 of the first silicon carbon composite is 5 μm to 13 μm. If the volume average particle diameter Dv50 of the first silicon carbon composite is too large, it may limit the charging performance of the secondary battery. If the volume average particle diameter Dv50 of the first silicon carbon composite is too small, the first active layer becomes relatively brittle, which may cause cracks to occur in the negative electrode plate during charging, affecting the battery's performance. Alternatively, the volume average particle diameter Dv50 of the first silicon carbon composite is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or 13 μm. More preferably, the volume average particle diameter Dv50 of the first silicon carbon composite is 7 μm to 11 μm.

[0054] In some embodiments, the specific surface area of ​​the first silicon carbon composite is greater than or equal to 1 m 2 / g~8m 2 / g. If the specific surface area of ​​the first silicon carbon composite is too large, the cycle performance and storage performance may be unfavorable. If the specific surface area of ​​the first silicon carbon composite is too small, the porosity of the first silicon carbon composite may be relatively small, and further, the dynamic performance of the battery may be unfavorable. Optionally, the specific surface area of ​​the first silicon carbon composite is less than 1 m 2 / g, 2m 2 / g, 3m2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g or 8m 2 / g. Further optionally, the specific surface area of ​​the first silicon carbon composite is 1 m 2 / g~5m 2 / g.

[0055] In some embodiments, the mass percentage of the first silicon carbon composite in the first active layer is 5% to 50%. If the mass percentage of the first silicon carbon composite in the first active layer is too small, the improvement in the effect of improving the energy density of the battery is not significant. If the mass percentage of the first silicon carbon composite is too large, the improvement in the effect of improving the compaction density is not significant. Optionally, the mass percentage of the first silicon carbon composite in the first active layer is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 35%, 40%, 45%, or 50%.

[0056] In some embodiments, the mass percentage of the porous carbon substrate in the first silicon carbon composite is ≧40%. If the mass percentage of the porous carbon substrate in the first silicon carbon composite is too small, the electrical conductivity of the first silicon carbon composite may be unfavorable, and the battery performance may be unfavorable. If the mass percentage of the porous carbon substrate is too large, the mass percentage of the corresponding silicon-based material may be too low, and the improvement in battery energy density may not be significant. Optionally, the mass percentage of the porous carbon substrate in the first silicon carbon composite is 40% to 60%. More optionally, the mass percentage of the porous carbon substrate in the first silicon carbon composite may be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, or 60%, etc.

[0057] In some embodiments, the porosity of the porous carbon substrate is 30% to 60%. If the porosity of the porous carbon substrate is too low, the dynamic performance of the battery may be unfavorable. If the porosity of the porous carbon substrate is too high, the cycling and storage performance of the battery may be unfavorable. Optionally, the porosity of the porous material may be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, or 60%, etc.

[0058] In some embodiments, the mass percentage of the silicon-based material in the first silicon carbon composite is ≦60%. If the mass percentage of the silicon-based material in the first silicon carbon composite is too high, the voltage resistance of the first active layer may be poor. At the same time, if the mass percentage of the silicon-based material is too high, the expansion rate of the first silicon carbon composite material may increase, which may result in poor structural stability of the negative electrode plate during charging. Alternatively, the mass percentage of the silicon-based material in the first silicon carbon composite is 40% to 60%. More preferably, the mass percentage of the silicon-based material in the first silicon carbon composite is 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, or 60%, for example.

[0059] In some embodiments, the silicon-based material includes nanosilicon, and optionally, the nanosilicon has a grain size of ≦6 nanometers (nm). In the first silicon carbon composite, the nanosilicon has a relatively small grain size, which can provide good performance for the first silicon carbon composite. Optionally, the nanosilicon has a grain size of ≦5 nm, ≦4 nm, ≦3 nm, ≦2 nm, or ≦1 nm, etc.

[0060] As can be seen, the content of silicon and carbon elements in silicon carbon composites can be tested by the following method: first, the electrode plate is cut into a size of 6mm x 6mm, and then attached to an ion milling machine and cut at a voltage of 7.5kV for 30 minutes. Then, in accordance with the JY / T010-1996 test standard, a Sigma300 scanning electron microscope and energy spectrometer are used to scan the elements in the region, so as to obtain the content ratio of silicon and carbon elements in the silicon carbon composites.

[0061] In some embodiments, the negative electrode active layer further comprises a second active layer located on a surface of the first active layer away from the negative electrode current collector, the second active layer comprising second graphite. The provision of the second active layer can further improve the overall compaction density of the negative electrode plate.

[0062] Optionally, the surface of the second graphite is coated with a carbon coating layer. In this case, the provision of the carbon coating layer can improve the overall conductivity of the second graphite and the rapid charging performance of the secondary battery. Optionally, the thickness of the carbon coating layer is 10 nm to 300 nm. For example, the thickness of the carbon coating layer is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm. More preferably, the thickness is 20 nm to 100 nm.

[0063] In some embodiments, the second graphite includes secondary particles. The introduction of secondary particles can further improve the charging performance of the secondary battery. Optionally, the number ratio of secondary particles in the second graphite is ≧50%. Even more optionally, the number ratio of secondary particles in the second graphite is ≧50%, ≧60%, ≧70%, ≧80%, or ≧90%, etc. Even more optionally, the second graphite is secondary particles.

[0064] In some embodiments, the volume average particle diameter Dv50 of the second graphite is smaller than the volume average particle diameter Dv50 of the first graphite. The relatively small volume average particle diameter Dv50 of the second graphite can reduce the lithium ion transport pathways, which is advantageous for improving the dynamic performance of the negative electrode plate and further improving the fast charging performance of the battery. Optionally, the volume average particle diameter Dv50 of the second graphite is 9 μm to 15 μm. For example, the volume average particle diameter Dv50 of the second graphite is 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm. More preferably, the volume average particle diameter Dv50 of the second graphite is 11 μm to 13 μm.

[0065] In some embodiments, the specific surface area of ​​the second graphite is greater than the specific surface area of ​​the first graphite, which is advantageous for improving the cycling performance of the battery. Optionally, the specific surface area of ​​the second graphite is greater than or equal to 0.8 m 2 / g~1.6m 2 For example, the specific surface area of ​​the second graphite is 0.8 m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or 1.6m 2 / g. More preferably, the specific surface area of ​​the second graphite is 1 m 2 / g~1.4m 2 / g.

[0066] In some embodiments, the second graphite comprises synthetic graphite, which can further improve the cycling performance of the battery.

[0067] In some embodiments, the second active layer further comprises a second silicon carbon composite. The second active layer further comprises a second silicon carbon composite, which can further improve the energy density of the secondary battery.

[0068] Optionally, the material of the second silicon carbon composite includes the material of the first silicon carbon composite. For example, the second silicon carbon composite includes a porous carbon substrate and a silicon-based material located in the pores of the porous carbon substrate. The volume average particle size Dv50 of the second silicon carbon composite is 5 μm to 13 μm, and optionally 7 μm to 11 μm. The specific surface area of ​​the second silicon carbon composite is 1 m 2 / g~8m 2 / g, and selectively 1m 2 / g~5m 2 / g. The mass percentage of the porous carbon substrate in the second silicon carbon composite is ≧40%, and optionally 40% to 60%. The porosity of the porous carbon substrate is 30% to 60%. The mass percentage of the silicon-based material in the second silicon carbon composite is ≦60%, and optionally 40% to 60%. The silicon-based material includes nanosilicon, and the crystal grain size of the nanosilicon is ≦6 nm. Optionally, the corresponding characteristics of the second silicon carbon composite can be correspondingly selected from the characteristics of the first silicon carbon composite described above.

[0069] As can be seen, the second silicon carbon composite is the same as the first silicon carbon composite.

[0070] In some embodiments, the mass percentage of the second silicon carbon composite in the second active layer is 5% to 50%. If the mass percentage of the second silicon carbon composite in the second active layer is too small, the improvement in the effect of improving the battery's energy density is not significant. If the mass percentage of the second silicon carbon composite is too large, the improvement in the effect of improving the compaction density is not significant. Optionally, the mass percentage of the second silicon carbon composite in the second active layer is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 35%, 40%, 45%, or 50%.

[0071] In some embodiments, the silicon carbon composite may be fabricated by depositing a silicon-based material into the pores of a porous carbon substrate. Optionally, the silicon-based material may be deposited into the pores of the porous carbon substrate by vapor deposition to further obtain the silicon carbon composite.

[0072] Optionally, the method for producing a silicon carbon composite includes: S101: A porous carbon substrate is placed in a vapor deposition furnace, and while the furnace body is rotating, the furnace is purged with an inert gas and preheated to 200 to 300 degrees Celsius (°C). Optionally, the porosity of the porous carbon substrate is 30 to 60%. Optionally, the inert gas includes at least one of nitrogen gas and argon gas. Optionally, the porous carbon substrate includes at least one of activated carbon, biomass carbon, and resin carbon.

[0073] S102: A mixed gas of a silicon source gas and an inert gas is introduced at a constant rate, and the pressure inside the furnace is controlled to be in a slightly positive pressure range. Optionally, the volume fraction of the silicon source gas in the mixed gas is 5% to 30%. Optionally, the pressure inside the furnace is controlled to be 200 Pascals (Pa) to 600 Pa higher than standard atmospheric pressure. Optionally, the silicon source gas includes at least one of monosilane and disilane.

[0074] S103: The temperature was then raised to 500°C to 700°C, and deposition was carried out for 2 hours to 12 hours.

[0075] S104: The silicon source gas is closed, the temperature is adjusted to 600°C to 800°C, and the carbon source gas is introduced and deposited for 2 to 12 hours. The silicon carbon composite is removed from the furnace and sieved to obtain a silicon carbon composite. Optionally, the volume fraction of the carbon source gas in the mixed gas is 5% to 20%. Optionally, the carbon source gas includes at least one of methane, ethylene, and acetylene.

[0076] Yet another embodiment of the present application provides a power consuming device, the power consuming device including the secondary battery described above.

[0077] The secondary battery and power consuming device of the present application will now be described with appropriate reference to the drawings.

[0078] A typical secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During charging and discharging, active ions shuttle between the positive and negative electrodes, absorbing and desorbing. The electrolyte serves to conduct ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0079] positive electrode plate The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0080] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode active material layer is disposed on one or both of the two facing surfaces of the positive electrode current collector.

[0081] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be obtained by forming a metal material on a polymer substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. Non-limiting examples of the polymer substrate in the positive electrode current collector may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0082] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. As a non-limiting example, the positive electrode active material may include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and a modified compound thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of the lithium transition metal oxide may include, but are not limited to, one or more of lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Non-limiting examples of lithium-containing phosphates of the olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composite, lithium manganese phosphate, lithium manganese phosphate and carbon composite, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite, and modified compounds thereof. Non-limiting examples of lithium cobalt oxides may include LiCoO2, non-limiting examples of lithium nickel oxides may include LiNiO2, non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc., and non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn0.2 O2(NCM 622 (may be abbreviated as "LiNi") 0.8 Co 0.1 Mn 0.1 O2(NCM 811 A non-limiting example of lithium nickel cobalt aluminum oxide is LiNi 0.8 Co 0.15 Al 0.05 May contain O2.

[0083] In some embodiments, the positive electrode active material layer may further include an adhesive. Non-limiting examples of the adhesive include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0084] In some embodiments, the positive electrode active material layer may further include a conductive agent, and the conductive agent may include, by way of non-limiting example, one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, a positive electrode plate can be manufactured in the following manner. Components for manufacturing the positive electrode plate, such as a positive electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent to form a positive electrode slurry. The positive electrode slurry is then applied to at least one surface of a positive electrode current collector, followed by drying, cold pressing, and other processes to obtain a positive electrode plate. The type of solvent may be selected from any one of the above-described embodiments, such as, but not limited to, N-methylpyrrolidone (NMP). The surface of the positive electrode current collector to which the positive electrode slurry is applied may be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The surface of the positive electrode current collector to which the positive electrode slurry is applied may be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry may be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted from 5,000 millipascals per second (mPa·s) to 25,000 mPa·s. When applying the positive electrode slurry, the applied area density (excluding the solvent) is 15 milligrams per square centimeter (mg / cm). 2 )~35mg / cm 2 The positive electrode plate may have a compacted density of 3.0 grams per cubic centimeter (g / cm 3 )~3.6g / cm 3 and optionally 3.3 g / cm 3 ~3.5g / cm 3 may be.

[0086] Negative electrode plate The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0087] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in the thickness direction thereof, and the negative electrode active material layer is disposed on one or both of the two facing surfaces of the negative electrode current collector.

[0088] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, copper foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be obtained by forming a metal material on a polymer substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. Non-limiting examples of the polymer substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0089] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. Non-limiting examples of the negative electrode active material include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one or more of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, stannate compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination.

[0090] In some embodiments thereof, the negative electrode active material layer optionally further includes an adhesive, which may include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0091] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0092] In some of the embodiments, the negative electrode active material layer optionally further contains other additives, such as a thickener (eg, carboxymethylcellulose sodium (CMC-Na)).

[0093] In some embodiments, a negative electrode plate can be manufactured in the following manner. Components for manufacturing the negative electrode plate, such as a negative electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (non-limiting examples of which include deionized water) to form a negative electrode slurry. The negative electrode slurry is then applied to at least one surface of a negative electrode current collector, followed by processes such as drying and cold pressing to obtain a negative electrode plate. The surface of the negative electrode current collector to which the negative electrode slurry is applied may be a single surface of the negative electrode current collector, or may be two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry may be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature may be adjusted to 2000 mPa·s to 10000 mPa·s. When the negative electrode slurry is applied, the application unit area density (excluding the solvent) is 75 grams per square meter (g / m 2 )~220g / m 2 The negative electrode plate may have a compaction density of 1.0 g / cm 3 ~1.8g / cm 3 may be.

[0094] electrolyte The electrolyte serves to conduct ions between the positive and negative electrodes. The present application does not particularly limit the type of electrolyte, and it may be selected according to needs. For example, the electrolyte may be liquid, gel, or all solid.

[0095] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0096] In some embodiments thereof, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPOF), lithium difluoro(oxalato)borate (LiDFOB), lithium difluoro(oxalato)borate (LiBOB), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0097] In some of these embodiments, the solvent is ethylene carbonate (EC, [ka] ), propylene carbonate (PC, [ka] ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate ( [ka] ), fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0098] In some embodiments, the electrolyte solution may further optionally contain additives. For example, the additives may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may further include additives that can improve some battery performance, such as an additive that improves battery overcharge performance or an additive that improves battery high-temperature or low-temperature performance.

[0099] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0100] Separator In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator with good chemical stability and mechanical stability may be selected.

[0101] In some embodiments, the separator may be made of one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitation.

[0102] In some embodiments, the thickness of the separator is between 6 μm and 40 μm, and optionally between 12 μm and 20 μm.

[0103] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be wound or stacked to form an electrode assembly.

[0104] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0105] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-like pouch. The material of the pouch may be plastic, and non-limiting examples of the plastic may include one or more of polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0106] A secondary battery includes at least one battery cell, and may include one or more battery cells.

[0107] In this application, unless otherwise specified, the term "battery cell" refers to a basic unit capable of realizing the mutual conversion of chemical energy and electrical energy, and generally includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During charging and discharging of the battery, active ions shuttle between the positive electrode plate and the negative electrode plate, absorbing and desorbing. The electrolyte serves to conduct the active ions between the positive electrode plate and the negative electrode plate.

[0108] The present application does not particularly limit the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, Figure 1 shows an example of a battery cell 1 with a square structure.

[0109] In some embodiments, referring to FIG. 2 , the exterior body may include a case 11 and a cover plate 13. Here, the case 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and side plate together form a surrounding accommodating cavity. The case 11 has an opening communicating with the accommodating cavity, and the cover plate 13 can be installed to cover the opening to seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is packaged in the accommodating cavity. An electrolyte is impregnated into the electrode assembly 12. The number of electrode assemblies 12 included in the battery cell 1 may be one or more, and those skilled in the art can select the number according to actual needs.

[0110] The secondary battery may be a battery module or a battery pack.

[0111] The battery module includes at least one battery cell. The number of battery cells included in the battery module may be one or more, and those skilled in the art may select an appropriate number according to the application and capacity of the battery module.

[0112] In a battery module, the battery cells may be arranged in a row along the length of the battery module, or may be arranged in any other manner. Furthermore, the battery cells may be fastened together by fasteners.

[0113] Optionally, the battery module may further include a housing having an accommodating space, and the plurality of battery cells are accommodated in the accommodating space.

[0114] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and those skilled in the art can select an appropriate number depending on the application and capacity of the battery pack.

[0115] The battery pack may include a battery box and a plurality of battery modules installed in the battery box. The battery box includes an upper housing and a lower housing, and the upper housing may be covered by a lid to form a sealed space for accommodating the battery modules. The plurality of battery modules may be arranged in the battery box in any manner.

[0116] The present application also provides a power consuming device including a secondary battery according to the present application. The secondary battery can be a power source for the power consuming device and can also be an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship, a satellite, an energy storage system, etc. Here, the mobile device may be, for example, a mobile phone, a laptop, etc., and the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited to these.

[0117] A secondary battery may be selected as the power consuming device depending on its usage demand.

[0118] 3 shows an example of a power consumption device 2. The power consumption device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the demand for high power output and high energy density of the secondary battery of the power consumption device, a battery pack or a battery module may be employed.

[0119] Other examples of the device may include a mobile phone, a tablet computer, a laptop computer, etc. These devices are generally required to be thin and lightweight, and may use a secondary battery as a power source.

[0120] In order to make the technical problems, technical solutions, and beneficial effects solved by the present application clearer, the present application will be described in more detail below in conjunction with examples and drawings. Obviously, the described examples are only some of the examples of the present application, and not all of the examples. The following description of at least one exemplary embodiment is merely illustrative in nature and does not constitute any limitation on the present application and its applications. All other embodiments obtained by those skilled in the art based on the examples in the present application without any creative effort are within the scope of protection of the present application.

[0121] Unless specific techniques or conditions are specified in the examples, they are performed according to the techniques or conditions described in the literature or in accordance with the product instructions. Unless the manufacturer is specified, reagents or equipment used are all commercially available products.

[0122] Secondary battery manufacturing method: (1) Manufacturing of silicon carbon composites S101: A biomass porous carbon substrate with a porosity of 50% was placed in a vapor deposition furnace, and the furnace was purged with nitrogen gas while rotating and heated to 200°C in advance.

[0123] S102: A mixed gas of silane gas and nitrogen gas was introduced at a ratio of 1:4, and the pressure inside the furnace was controlled to be 300 Pascals (Pa) higher than standard atmospheric pressure.

[0124] S103: The temperature was then raised to 500°C and deposition was continued for 8 hours.

[0125] S104: The silane gas was closed, the temperature was adjusted to 620°C, and acetylene gas was introduced at a flow rate of 10%. The deposition was continued for 2 hours. The silicon carbon composite was removed from the furnace and sieved to obtain a silicon carbon composite, which included a porous carbon substrate and a silicon-based material located in the pores of the porous carbon substrate.

[0126] (2) Manufacturing of negative electrode plates The first graphite, the first silicon carbon composite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose, and the adhesive styrene butadiene rubber were mixed, and then deionized water was added. After stirring under vacuum, a first slurry with a solids content of 49% was obtained.

[0127] The second graphite, the second silicon carbon composite, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose, and the adhesive styrene butadiene rubber were mixed, and then deionized water was added. After stirring under vacuum, a second slurry with a solids content of 49% was obtained.

[0128] 1. When the negative electrode plate contains only the first active layer, the first slurry is coated onto a copper foil current collector, dried at 85°C, then cold pressed, trimmed, slit, cut, and finally dried at 120°C under vacuum for 12 hours to obtain a negative electrode plate.

[0129] When the negative electrode plate contained both a first active layer and a second active layer, the first slurry was applied to a copper foil current collector and dried at 85°C to form a first active layer on the current collector. The second slurry was then applied to the first active layer and dried at 85°C, followed by cold pressing, trimming, slitting, and cutting. Finally, the negative electrode plate was dried in a vacuum at 120°C for 12 hours.

[0130] (3) Manufacturing of positive electrode plates The positive electrode active material NCM, adhesive polyvinylidene fluoride, and conductive agent acetylene black were mixed in a ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) was added and stirred to form a positive electrode slurry. The positive electrode slurry was uniformly applied to a positive electrode current collector aluminum foil, dried, and cold-pressed to obtain a positive electrode plate.

[0131] (4) Electrolyte production Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed in a volume ratio of 20:20:60 to form an organic solvent. LiPF was then dissolved in the organic solvent, and fluoroethylene carbonate (FEC) was added. The concentration of LiPF in the electrolyte was 1 mole / liter (mol / L), and the mass percentage content of FEC was 5 wt%.

[0132] (5) Separator: A PP separator was used.

[0133] (6) The negative electrode plate, separator, and positive electrode plate were stacked in this order and wound to obtain a wound battery core. The battery core's design capacity was 4.5 ampere-hours (Ah). The battery core was placed in a rectangular aluminum case, dried, and then injected with an electrolyte. After going through processes such as packaging, standing, chemical formation, aging, secondary packaging, and capacity, a secondary battery was obtained.

[0134] The compositions of the negative electrode plates in the examples and comparative examples are as shown in Table 1.

[0135] Test Example (1) Battery energy density test: At 25°C, the manufactured battery was fully discharged at 1C, then fully charged at 1C, and fully discharged at 1C, and the actual discharge energy at this time was recorded. At 25°C, the effective length / width / thickness of the battery core 1C in a fully charged state was measured, and the effective volume V was calculated. The ratio of the actual discharge energy D of the battery 1C to the effective volume V of the battery core was the actual energy density E of the battery, E = D / V, where D is in watt-hours (Wh) and V is in liters (L).

[0136] (2) Electrode plate structural stability test: The obtained battery was fully charged at 1C, disassembled to obtain the negative electrode plate, folded along the large surface in the horizontal direction, and roll-pressed once along the fold line with a 1 kg standard roll press tool. The folding and roll-pressing operations were repeated three times to check the light transmission or fracture status of the electrode plate at the fold point. The severity was classified into four levels: 1. fracture: electrode plate breakage; 2. serious light transmission: >5 light transmission points; 3. slight light transmission: 1-5 light transmission points; 4. no light transmission.

[0137] (3) Battery cycle performance test: The manufactured battery was cycled at 0.5C / 1C at 25°C to determine the number of cycles at which the battery was attenuated to 80%, i.e., the cycle performance of the corresponding battery.

[0138] (4) Battery charging capacity test: The battery core was fully charged at a rate of 1.2C, and then disassembled after full charge to check the lithium deposition status on the anode interface. Four lithium deposition levels were defined based on the lithium deposition area percentage: 1. No lithium deposition, 2. Lithium deposition area <10%, mild lithium deposition, 3. Lithium deposition area 10%-30%, moderate lithium deposition, and 4. Lithium deposition area >30%, severe lithium deposition.

[0139] [Table 1-1] [Table 1-2]

[0140] As can be seen, in Table 1, the units of Dv50 are μm. The units of specific surface area are m 2 / g. The unit of the thickness of the carbon coating layer is nm. The unit of the energy density is Wh / L. The unit of the battery cycle performance is cycles. In the particle composition of the first graphite, "primary 90% + secondary 10%" means that in the first graphite, the proportion of the number of primary particles is 90% and the proportion of the number of secondary particles is 10%. In the particle composition of the second graphite, "primary 50% + secondary 50%" means that in the first graphite, the proportion of the number of primary particles is 50% and the proportion of the number of secondary particles is 50%.

[0141] As can be seen from Table 1, compared to Comparative Example 1, the negative electrode plates in Examples 1 to 3 have better structural stability, indicating that the structural stability of the negative electrode plate can be improved when the first graphite has an appropriate flatness.

[0142] Compared with Example 5, the negative electrode plates in Examples 1 to 3 have better structural stability, which indicates that when the primary particles in the first graphite have an appropriate proportion, the structural stability of the negative electrode plate can be improved.

[0143] Compared with Example 2, the battery corresponding to Example 6 has better charging ability, which indicates that when the second graphite is present, the corresponding battery can obtain better charging performance.

[0144] Compared with Comparative Examples 2 to 4, the battery corresponding to Example 1 can more effectively achieve a good overall balance between good energy density, structural stability of the negative electrode plate, cycle performance, and charging performance.

[0145] The technical features of the embodiments described above can be combined in any combination. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, any combination should be considered within the scope of the present specification.

[0146] The above examples only show some embodiments of the present application, and although the descriptions are more specific and detailed, they should not be understood as limiting the scope of the invention patent. It should be noted that those skilled in the art can make further modifications and improvements without departing from the concept of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application patent shall be governed by the appended claims. [Explanation of symbols]

[0147] 1 secondary battery, 11 case, 12 electrode assembly, 13 cover plate, 2 power consumption device.

Claims

1. 1. A secondary battery comprising: a negative electrode plate, the negative electrode plate comprising: a negative electrode current collector; and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a first active layer comprising first graphite and a first silicon-carbon composite, the first graphite having a flatness of 2 or greater, and the first silicon-carbon composite comprising a porous carbon substrate and a silicon-based material located in pores of the porous carbon substrate.

2. 2. The secondary battery according to claim 1, wherein the flatness of the first graphite is 2.5 to 20, and optionally 4 to 16.

3. the first graphite comprises primary particles; Optionally, the number ratio of the primary particles in the first graphite is ≧90%.

4. The first graphite is (1) The first graphite has a volume average particle diameter Dv50 of 12 μm to 18 μm, and optionally 14 μm to 16 μm; (2) The specific surface area of ​​the first graphite is 0.6 m ２ / g to 1.4m ２ / g, and optionally 0.8m ２ / g to 1.2m ２ The secondary battery according to claim 1 , wherein the secondary battery satisfies at least one of the following characteristics:

5. The first graphite includes artificial graphite and / or natural graphite, Optionally, the first graphite includes natural graphite, and a mass percentage of the natural graphite in the first graphite is ≦20%.

6. The first silicon carbon composite is (1) The first silicon carbon composite has a volume average particle diameter Dv50 of 5 μm to 13 μm, and optionally 7 μm to 11 μm; (2) The specific surface area of ​​the first silicon carbon composite is 1 m ２ / g~8m ２ / g, and optionally 1m ２ / g to 5m ２ / g, (3) A mass percentage of the first silicon carbon composite in the first active layer is 5% to 50%.

7. The porous carbon substrate is (1) The mass percentage of the porous carbon substrate in the first silicon carbon composite is ≧40%, and optionally 40% to 60%; (2) The secondary battery according to any one of claims 1 to 6, wherein the porosity of the porous carbon substrate is 30% to 60%.

8. The silicon-based material is (1) The mass percentage of the silicon-based material in the first silicon carbon composite is ≦60%, and optionally 40% to 60%; (2) The secondary battery according to any one of claims 1 to 7, wherein the silicon-based material contains nanosilicon, and optionally, the crystal grain size of the nanosilicon is ≦6 nm.

9. 9. The secondary battery according to claim 1, wherein the negative electrode active layer further comprises a second active layer, the second active layer being located on a surface of the first active layer remote from the negative electrode current collector, and the second active layer comprising second graphite.

10. a carbon coating layer is coated on the surface of the second graphite; 10. The secondary battery according to claim 9, wherein the thickness of the carbon coating layer is preferably 10 nm to 300 nm, and more preferably 20 nm to 100 nm.

11. the second graphite includes secondary particles, Optionally, the number ratio of the secondary particles in the second graphite is ≧50%, and optionally 50% to 90%.

12. The second graphite is (1) The volume average particle diameter Dv50 of the second graphite is smaller than the volume average particle diameter Dv50 of the first graphite, Alternatively, the volume average particle diameter Dv50 of the second graphite is 9 μm to 15 μm, and more preferably 11 μm to 13 μm; (2) The specific surface area of ​​the second graphite is larger than the specific surface area of ​​the first graphite; Optionally, the specific surface area of ​​the second graphite is 0.8 m ２ / g to 1.6m ２ / g, and more preferably 1m ２ / g to 1.4m ２ The secondary battery according to claim 9 , wherein the secondary battery satisfies at least one of the following characteristics:

13. the second active layer further comprises a second silicon carbon composite; Optionally, the second silicon carbon composite material comprises the first silicon carbon composite material; Optionally, a mass percentage of the second silicon carbon composite in the second active layer is 5% to 50%.

14. A power consuming device comprising a secondary battery according to any one of claims 1 to 13.

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